1. Field of the Invention
The present invention relates to a semiconductor device which transmits signals among, e.g., a plurality of logical circuits operated by different voltages.
2. Description of the Related Art
Conventionally, in the case of transmitting signals among a plurality of logical circuits of different operation voltages, level conversion circuits have been disposed among the logical circuits. For example, the level conversion circuit converts voltage amplitude V1 of an input signal into higher voltage amplitude V2 to output it. That is, the level conversion circuit outputs a signal of a low level (“L”=0 V) when an input signal is a low level (“L”=0 V), and a signal of a high level (“H”=V2>V1) when an input signal is a high level (“H”=V1) (e.g., p. 543 of “CMOS Digital Integrated Circuit, Analysis and Design (Second edition)” by Sung-Mo Kang, Yusuf Leblebici, McGraw-Hill, 1999).
This circuit has a problem that transmission time from supplying of the input signal to outputting of the output signal is slower when a difference between the voltages V1 and V2 is large as compared with that when a difference therebetween is small. In other words, there is a problem that time until a change of the input signal from “L” to “H” or “H” to “L” after a change of the input signal from “L” to “H” or “H” to “L” is changed depending on a difference between the voltages V1 and V2.
There has recently been developed a system-on-chip (SoC) device which comprises a plurality of logical circuits operated by a plurality of voltages in one chip. To transmit signals among the logical circuits which belong to different voltage domains, this SoC device needs a level conversion circuit. In the case of using the conventional circuit, however, as a difference occurs in signal transmission time depending on a difference between operation voltages, a certain margin must be provided to signal transmission timing at a design stage. Consequently, it has been difficult to increase an operation speed of the SoC device. Therefore, there is a demand for a semiconductor device which can transmit signals among circuits belonging to different voltage domains at a high speed.